Chemistry is the science which deals with materials, their properties and the transformations they undergo. So chemistry is the study of the composition and properties of matter, their changes, the conditions under which such changes take place, and the energy changes which accompany them.
Chemistry is concerned with the nature of fire and the structure of water, it deals with colours, catalysis and crystal structure, with physical properties and chemical reactivity.
Chemistry is one of the fundamental sciences. It plays an important part in the development of biochemistry, physics, geology and many other fields of science. Chemistry’s origin goes back to ancient times, with the manufacture of bronze, iron, ceramics, glass.
Everyone now understands the importance of chemistry. The future of chemistry is practically unlimited. Rapid development of chemical industry will make it possible to create many new goods, machines, plastics, polymers; it will help to understand many new phenomena.
In your study of chemistry you will learn many things about substances, compounds, materials, chemical and physical changes, chemical properties, reactions and many other interesting and important things. It is to be remembered that:
1. Chemistry is the study of substances, their structure, properties, and their reactions.
2. Matter exists as solids, liquids, or gases.
3. Homogeneous material is material with the same properties throughout.
4. Heterogeneous material is material consisting of parts with different properties.
5. Compound is a substance that can be decomposed into two or more substances.
6. Substance is a homogeneous species of matter with definite chemical composition.
7. Chemical reactions are the processes that convert substances into other substances.
8. Alloy is a metallic material containing two or more elements.
Words to be remembered:
to deal with heterogeneous
to undergo chemical composition
origin to convert
compound to contain
SOME FACTS ABOUT CHEMISTRY
The science of chemistry deals with substances. Chemistry is the investigation and discussion of the properties of substances.
Common examples of substances are: water, sugar, salt, copper, iron and many others.
Chemists study substances in order to learn as much as they can about their properties and about the reactions that change them into other substances. This knowledge is very important as it can make the world a better place to live in, it ñan make people happier, it can raise their standard of living.
Chemists discovered many laws, investigated many important phenomena in life. They produced many artificial substances which have valuable properties.
Chemistry has two main aspects: descriptive chemistry, the discovery of chemical facts, and theoretical chemistry, the formulation of theories.
The broad field of chemistry may also be divided in other ways. An important division of chemistry is that into the branches of organic chemistry and inorganic chemistry.
Organic chemistry is the chemistry of the compounds of carbon that occur in plants and animals.
Inorganic chemistry is the chemistry of the compounds of elements other than carbon. Both of these branches of chemistry is in part descriptive and in part theoretical.
Analytical chemistry deals with the methods of separation. Synthetic chemistry deals with the methods by which complex bodies can be built from simpler substances. Physical chemistry deals with changes of state and with the motions of molecules. But at present time the scientists don’t maintain this definition.
The discovery of X-rays, an electron, and radioactivity marked a new era in all sciences and in chemistry. It was a very important discovery in science. It plays an important part in the development of geology and physiology, in technology and engineering.
Chemistry deals with medicine and agriculture as they are all concerned with the properties and changes of chemical substances.
Words to be remembered:
in order to motion
phenomena to be concerned with
artificial carbon compounds
SOME FACTS ABOUT ATOMS (I)
An atom may be spoken of as the smallest particle of any substance. If atoms cannot be seen it does not necessarily mean that they do not exist. It indicates that any particle, if present, must be extremely small. There are methods by means of which the sizes of atoms and their arrangement in molecules can be determined. One of these methods uses X-ray diffraction.
The results of a number of investigations show that when atoms are in contact with other atoms in molecules, their radius is as much as 0,1· m(0,1nm).
Some idea of how small atoms are can be obtained by imagining one million copper atoms / radius = 0,13· m (0,13 nm). If these copper atoms are stacked one on the top of the other, the pile will be as high as the full stop at the end of this sentence.
In the course of many investigations, chemists came to a conclusion that the atoms of different elements are all made essentially of three simple types of units, which were referred to as protons, neutrons, and electrons.
The following diagram shows us the constituents of the atoms. Atoms contain the following structural units:
Electrons Protons Neutrons
Charge –1, Charge +1, Zero charge,
very small relative relative mass 1 relative mass 1
Notes on the text:
a full stop - òî÷êà in the course of - â õîäå, ïðîöåññå
Words to be remembered:
particle by means of
to mean conclusion
to indicate constituent
SOME FACTS ABOUT ATOMS (II)
The position and numbers of these structural units in an atom is shown below:
Electrons fill the space around nucleus. Number of electrons = Atomic number. Very small nucleus. Number of protons = Atomic number. Number of protons + Number of neutrons = Relative atomic mass.
The numbers of electrons, protons, and neutrons in an atom of an element can be calculated if the atomic number and relative atomic mass of the element are known:
Number of electrons + Number of protons = Atomic number of element.
Number of protons + Number of neutrons =Relative atomic mass of element.
It was also found that many elements and compounds are composed of small numbers of atoms which are held together in a regular arrangement. These groups of atoms are referred to as molecules. The gas hydrogen, for example, is composed of pairs of hydrogen atoms and each pair is called a molecule and its formula is H2.
Another example is the compound carbon dioxide which is composed of molecules, the formula is CO2.
Words to be remembered:
space to be composed of
relative carbon dioxide
Note on the text:
regular arrangement - óïîðÿäî÷åííîå ðàñïîëîæåíèå
THE ATOMIC MODEL
The electron, the proton, and the neutron gather together into what can be called the atom.
Our concept of the atom derives from a series of observations. As a result of these observations, we now believe that an atom is composed of a cloud of electrons that revolve about a central core of protons or of protons plus neutrons. Repeated experiments, which were referred to above, show that every atom has the same number of electrons as well as protons. The positively charged protons form the nucleus of the atom, and balance the positive charges of the protons in the core of the atom. The neutrons are also found in the nucleus of the atom. The neutrons are also found in the nucleus of the atom.
An atom has already been spoken of as the smallest unit of an element. It is known that ninety-two elements occur in nature, and a number of others have been made by man in the laboratory. Every element is a special combination of protons, neutrons, and electrons. Each element is identified by the number of protons in its nucleus and is designated by a name and a symbol.
Element Number 1 is a combination of one proton and one electron. Long before its atomic structure was known, this element was referred to as hydrogen, or "water-former", because water forms when hydrogen burns in air. Its symbol is H. Hydrogen has the first place in the list of elements because it has one proton in its nucleus. Element 1 is followed by Element Number 2. It consists of two protons and two electrons. It was named helium, with the symbol He.